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ACCURACY OF POLYGRAPH TESTING AND ITS STATUS AS SCIENTIFIC EVIDENCE

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Abstract

Long-standing experience in using the polygraph to investigate criminal cases is a direct proof of its usefulness and practical accuracy. Opponents of polygraph testing argue, among others, that owing to its low accuracy, polygraph results should not be admitted as evidence in criminal cases. And indeed, the accuracy expressed as the ratio of accurate to inaccurate outcomes is a good measurement of the method's identification accuracy in forensic science. Generally, this method is admissible as evidence if its accuracy is at least at rates of 90% for evidential (court) purposes and not lower than 80% for investigative purposes, assuming that calculations do not include inconclusive results. The overall body of inconclusive results for a given method cannot exceed 20%. Polygraph tests are among those methods of forensic identification whose accuracy has been most thoroughly validated by methodologically different experimental methods and specific-incident testing, as a result of which accuracy of polygraph testing has been proved sufficient for the purposes of court trial, let alone police investigations. Despite the said accuracy being different for the Control Question Technique (CQT) and Concealed Information Test (CIT), it is generally high and parallel with many other scientifically validated forensic methods, sometimes even higher, as it generates fewer false positive errors. Irrespective of its validity or reliability, often the polygraph test is simply a useful investigative tool.

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Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.